Such bags are described, for example, in documents EP-A-00510010, EP-A-0102301, and EP-A-0479661.
Generally, the cursors have two lateral flanges interconnected via a web and which co-operate with an elongate central tongue placed between the closure strips to define two converging passages for the interfittable complementary closure strips. Thus, when the direction of displacement of the cursor relative to the closure strips tends to force the closure strips into engagement, the bag is closed. In contrast, when the cursor is displaced in the opposite direction, the bag is opened by means of the central tongue separating the closure strips.
Such bags that are actuated both for opening and for closing by a cursor have already given good service.
Cursors make it easier to open and close bags. The presence of a cursor is particularly well received by the elderly or the visually handicapped.
Nevertheless, the majority of known cursor-fitted bags do not give complete satisfaction. In particular, most of such bags are not completely leakproof when the strips are in the closed position. Leakage is due to the fact that the strips remain separate ahead of the cursor because of the presence of the central tongue placed between the closure strips.
Nevertheless, leakproofing is required in numerous applications, in particular, but in non-limiting manner, for the bags which are used for freezing foodstuffs.
Attempts have been made to remedy that drawback by making a cutout in the closure strips or in the film close to the end which receives the cursor when the bag is in its closed position, so that the tongue of the cursor penetrates into the cutout or is situated between portions of film that are independent of the closure strips, thereby enabling the strips to be properly engaged over their entire length when in the closed position. Examples of such means are to be found in documents U.S. Pat. Nos. 5,067,208, 5,442,837, and 5,020,194.
Nevertheless, the means proposed in that context turn out to be very complex. And even so, they do not always provide bags that are completely leakproof. Furthermore, they present the major drawback of not retaining the cursor properly and consequently of running the risk, for example, of the cursor being swallowed by young children.
Other solutions have also been proposed in which the central tongue of the cursor is mounted to move relative to the cursor between an active position in which said tongue is placed between the closure strips, and a retracted position in which the tongue is at a distance from the closure strips. An example of such means is to be found in document WO-A-98/23493.
In theory, those solutions make it possible to improve bag leakproofing. Nevertheless, in practice, they turn out to be too complex since leakproofing is not guaranteed if the user forgets to move the cursor tongue into its retracted position. In addition, those solutions can sometimes be rather unreliable insofar as the tongue can become completely separated from the cursor after it has been handled frequently.